Tuning Structure-Function Properties of Ï-Conjugated Superstructures

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Tuning Structure-Function Properties of #-Conjugated Superstructures by Redox-Assisted Self-Assembly Kaixuan Liu, Adam Levy, Chuan Liu, and Jean-Hubert Olivier Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b00518 • Publication Date (Web): 02 Mar 2018 Downloaded from http://pubs.acs.org on March 3, 2018

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Chemistry of Materials

Tuning Structure-Function Properties of π-Conjugated Superstructures by Redox-Assisted Self-Assembly Kaixuan Liu,† Adam Levy,† Chuan Liu† and Jean-Hubert Olivier*,† †Department of Chemistry, University of Miami, Coral Gables, Florida 33146-0431 ABSTRACT: Controlling structure-function properties of hierarchical assemblies that feature stacks of π-conjugated building blocks represents an important challenge to engineer optoelectronic materials. In this regard, the development of new tools to navigate the free energy landscape of supramolecular assembly can lead to the creation of kinetically trapped superstructures equipped with emergent electronic properties. In the present contribution, we demonstrate that redox-assisted self-assembly of supramolecular polymers built from water-soluble perylene diimide enforces formation of superstructures with optoelectronic properties not manifested in parent assemblies. Leveraging on a theoretical model developed for H-aggregates in semiconducting polymers, freeexciton bandwidth has been calculated and increases by more than 30% in kinetically trapped superstructures (380 meV) when compared to initially prepared assemblies (290 meV). Electronic structure of intermediate assemblies is believed to perturb intermolecular interactions that regulate the conformation of initially prepared architectures. In addition to offering a means to modulate superstructure electronic properties, intermediate states can be further manipulated by thermal treatment to enable the formation of hierarchical nano-to-mesoscale materials. Investigation of their solid-state morphologies using atomic force microscopy reveals long aspect ratio nanowires spanning micro-to-mesoscale dimensions. Such morphological changes combined with novel electronic properties indicate that structure-function properties of supramolecular constructs can be modulated by redox-assisted selfassembly.

these intermediate states will enable the exploration of new pathways in self-assembly free energy landscape as it can engender, for example, novel electrostatic interaction patterns between π-conjugated building blocks not possible by a conventional approach. Materials created in this manner remain elusive, yet they can manifest emergent structure-function properties that contrast those observed in assemblies formed through non-perturbed intermediates. Self-assembly of π-conjugated building blocks in nonaqueous media can produce shallow kinetic states that evolves overtime towards lower energetic states (either local or global minimum).20 Dynamic aspects of such processes may limit the extent to which structure-function properties of selfassemblies can be precisely controlled and modulated. In contrast, kinetic states accessed by self-assembled π-surfaces in water are characterized by high energy barriers that engender formation of stable superstructures with conformations that are

INTRODUCTION The optical and electrical properties of superstructures that feature stacks of π-conjugated building blocks have fueled the interest to exploit this class of materials as light harvesting media,1-2 charge migration conduits,3-5 and spin transport domains.6 While these pioneering studies have established important benchmarks, the efficiency with which organic selfassemblies transport energy remains several orders of magnitude lower than that of inorganic benchmarks. Close examination of parameters that regulate structure-function properties of π-conjugated supramolecular polymers reveals that electrostatic interactions between neighboring building blocks play a cardinal role in dictating superstructure conformation, and in turn, the magnitude of which frontier molecular orbitals overlap.7 Consequently, such materials are neither structurally nor electronically configured for maximum efficiency.8-9 Recent examples have unambiguously demonstrated that structure-function properties of organic self-assemblies can be modulated, to some extent, by navigating the aggregation free energy landscape opening fresh opportunities to regulate the optoelectronic properties of organic materials.10-14 This process coined pathway selection defines a new set of tools to reconfigure superstructure conformation when migrating from the equilibrium state (global energy minimum) to a kinetically trapped state (local energy minimum). Whether kinetic control is achieved by means of solvent processing,15 mechanical forces,16 heating/cooling cycles,14, 17-18 or chemical fuel,13 intermediate states (metastable and kinetic) that enable navigation between local minima are key components to regulate the transition from one kinetically trapped states to another.19 In this regard, the ability to modulate the electronic structure of

Figure 1. (A) Chemical structures of PDI-(H)2-OH and PDI(OTEG)2-OH building blocks exploited to explore redoxassisted self-assembly and probe superstructure reconfiguration. (B) Electrostatic potential maps of a representative PDI building block and corresponding π-conjugated superstructure plotted from DFT calculation (ωb97xd/cc-pvdz).

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preserved over time.21-23 While major contributions have advanced the understanding of the mechanisms that govern selfassembly of π-conjugated systems in aqueous media,24-26 strategies to modulate electronic structure of intermediate states to tune structure-function properties of superstructures are currently underexplored. In the present contribution, we demonstrate that redox-assisted self-assembly of supramolecular architectures built from water-soluble perylene diimide (PDI) units enables the formation of kinetically trapped assemblies for which free-exciton bandwidth has been increased by more than 30%. Congruent with the change of photophysical properties, a profound modification of superstructure morphology is observed at meso-to-macroscale dimensions suggesting nonnegligible perturbation of the intermolecular interactions between neighboring building blocks.

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system that adopts a bent conformation.33-34 When compared to PDI-(H)2-OH, higher chain elongation constant dictates formation of PDI-(OTEG)2-OH assembly and limits the elucidation of the corresponding supramolecular polymerization mechanism (see Figure S2 and associated discussion).

RESULTS AND DISCUSSION The extent to which electronic structure of intermediate states may be utilized to perturb structure-function properties of initially prepared PDI assemblies is explored by following the redox cycle in Scheme 1. Ground-state electronic absorption spectra (EAS) that summarize the reductive titrations of PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies by controlled addition of sodium dithionite solution at pH=12 in D2O are presented in Figure 2 and Figure S9 respectively. Examination of the EAS recorded for the unsubstituted PDI core upon addition of 1 eq. of reductant (Figure 2A) reveals spectral features at 732, 818 and 992 nm reminiscent of PDI radical anion.35 Similar to near infrared (NIR) transitions reported upon titration of water-soluble naphthalene diimide derivatives,36-38 the concomitant growth of a broad absorptive feature at 1650 nm is congruent with formation of radical π-anions and suggests non-negligible electronic communication between reduced PDI units. As observed in Figure 2B, further increase of reductant concentration up to 3.0 eq. leads to the appearance of novel transitions at 622 nm and 876 nm that contrast that of PDI radical anion. In addition, the rise of a transition beyond 2500 nm indicates formation of a new electronic state upon n-doping the origin of which is currently under investigation. These spectral features suggest that reduced PDI-(H)2-OH assembly remains under aggregated states. It is important to note that the emergent transitions centered at 622 nm, 876 nm and beyond 2500 nm differ drastically from the spectral signatures characteristic of solubilized PDI-derived dianion at 504, 539, and 613 nm (see section 4 in the supporting information). In aqueous media, the highenergy barrier characteristic of kinetically trapped assemblies provides necessary stabilization energy to counterbalance electrostatic repulsion between charged PDI-(H)2-OH building blocks preventing dismantlement of the superstructure under n-doped conditions. Reductive titration spectra of initially prepared PDI(OTEG)2-OH assembly in water are presented in Figure S9 and contrast these recorded for PDI-(H)2-OH derivative. While addition of 1 eq. of Na2S2O4 reductant generates aggregated PDI-(OTEG)2-OH radical anion, increase of reductant concentration up to 3.0 eq. with respect to PDI analyte is accompanied with the rise of absorptive features at 546 nm, 580 nm, and 648 nm that is reminiscent of aggregated PDI dianion (see section 4 in the supporting information for detailed explanation). When compared to non-functionalized PDI-(H)2-OH building blocks, water-soluble triethyleneglycol side chains featured on PDI-(OTEG)2-OH may favor partial dismantlement of corresponding π-conjugated assemblies upon electron injections, and hamper formation of emergent electronic states previously monitored in n-doped PDI-(H)2-OH assemblies. Based on the presented reductive titration experiments, reduced PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies (intermediate 1 - Scheme 1) possess different electronic properties that can be correlated to structural features of respective building blocks.

Scheme 1. Schematic representation of the redox cycles to produce redox-treated assembly and reconfigured superstructures from initially prepared assembly.

Bolstered by appealing optical properties, low-lying reduction states associated with unambiguous spectral signatures, and chemical stability over a wide range of pH and temperature, perylene diimide frameworks are ideal candidates to engineer superstructures relevant to modern optoelectronic applications.2 Only a handful of studies have reported perturbation of structure-function properties evinced by PDI-derived materials upon exposure to reductive conditions,13, 27-30 and molecular insights into parameters that govern such perturbation remain vastly elusive. The two PDI building blocks PDI(OTEG)2-OH and PDI-(H)2-OH represented in Figure 1A feature ammonium-derived side chains enabling these πconjugated platforms to exist as solubilized nanoscale objects in aqueous media (initially prepared assemblies – Scheme 1). As illustrated in Figure S1, isodesmic supramolecular polymerization best describes the assembly of PDI-(H)2-OH in water and is in agreement with previously established systems.31-32 Electrostatic potential maps of the unsubstituted PDI core presented in Figure 1B confirms that electrostatic interaction between the strongly electron withdrawing groups (red) and the more electron poor aromatic bay region (blue) is governing conformation of the PDI-derived equilibrium assemblies. To gain further insight into the impact of PDI structure on the self-assembly free energy landscape, PDI-(OTEG)2OH building blocks feature triethylene glycol side chains on the aromatic 1,7-positions. It is well-established that insertion of substituents on PDI 1,7-positions contorts the π-conjugated

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Figure 2. UV-vis-NIR steady state absorption spectra that chronicle the reductive titration of initially prepared PDI-(H)2-OH assembly with sodium dithionite (Na2S2O4) in D2O. Spectral evolution upon addition of (A) 0.00 to 1.36 eq. of reductant, and (B) 1.7 to 15 eq.; in brackets are the respective ionic strength for each titration point. Experimental conditions: initial [PDI-(H)2-OH] ∼0.23 mM; final [PDI(H)2-OH] 0.17 mM; argon atmosphere; T = 25°C; optical path length 2 mm.

To further elucidate the impact of intermediate 1 on the structure-function properties of π-conjugated self-assemblies, reduced PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies were neutralized by exposure to ambient air (Scheme 1 – step 2); the electronic properties of these redox-treated assemblies were investigated. When comparing the absorption profiles of initially prepared and redox-treated PDI-(OTEG)2-OH assemblies presented in Figure 3 C-D, no noticeable changes can be gleaned. As slight perturbation of superstructure conformation would transpire on EAS, this result indicates that intermediate PDI-(OTEG)2-OH assembly 1 does not impact structure-function properties of the supramolecular architectures. In sharp contrast, examination of the EAS recorded for the initially prepared and redox-treated PDI-(H)2-OH assemblies presented in Figure 3 A-B reveal a drastic redistribution of the oscillator strength between the 0-0, 0-1, and 0-2 vibronic lines centered at 555 nm, 501 nm, and 455 nm respectively. Such perturbation of the assembly electronic structure points towards the non-innocent role played by intermediate state 1 in scheme 1 and calls for further investigation. Congruent with the fact that H-aggregates best described the conformation of PDI-(H)2-OH and PDI-(OTEG)2-OH building blocks in respective superstructures (Figure 1B),39-42 we leveraged on an exciton model developed for H-aggregates in semiconducting polymers to quantify the extent to which building block interaction is perturbed upon n-doping the initially prepared assemblies.43-45 In this regard, the ratio of the 00 and 0-1 oscillator strength transitions can be exploited to

calculate the free-exciton bandwidth ExBW (see the experimental section). Table 1 summarizes the ExBW calculated for initially prepared and redox-treated assemblies. Please note that free-exciton bandwidth in H-aggregates is proportional to the electronic coupling between building blocks. As suggested by the EAS recorded for PDI-(OTEG)2-OH assemblies, negligible change in exciton bandwidth is observed when comparing initially prepared (ExBW = 402 meV) to redox-treated selfassemblies (ExBW = 425 meV). In sharp contrast, a significant increase of more than 30% of free-exciton bandwidth is calculated for redox-treated PDI-(H)2-OH superstructures (ExBW = 380 meV) when compared to parent assembly (ExBW = 290 meV). This augmentation of free-exciton bandwidth suggests an increase of electronic coupling between building blocks, and consequently a perturbation of the initially prepared assembly conformation. Since addition of reductant solution increases the ionic strength of analyzed solution and that increase of ionic strength is recognized to impact self-assembly conformation,46-47 it was critical to investigate control samples which mimic the ionic strength of redox-treated selfassemblies. As presented in Figure S10 and S11, no increase of exciton bandwidth can be elucidated when comparing control PDI-(H)2-OH and PDI-(OTEG)2-OH samples with ionic strength (2.65 M L-1) resembling that of redox-treated selfassemblies (2.70 M L-1). Examination of PDI-(H)2-OH and PDI-(OTEG)2-OH control samples confirms that the freeexciton bandwidth increase, exclusively evidenced in redoxtreated

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Figure 3. Electronic absorption spectra recorded for initially prepared PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies (A and C respectively), and redox-treated PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies (B and D respectively) in D2O at 20˚C ([PDI] = 2.2 x 10-4 M). Area under the curves in orange, purple, and green have been calculated by nonlinear spectral fitting and correspond to transition from the ground state S0 to the different vibronic state (0, 1, 2) within the S1 manifold.

PDI-(H)2-OH assembly, is not induced by perturbation of the solution ionic strength but is rather a property enforced by redox-assisted self-assembly.

Dynamic light scattering (DLS) and atomic force microscopy (AFM) were utilized to investigate the impact of redoxtreatment on the size and morphology of PDI-(H)2-OH and PDI-(OTEG)2-OH assemblies. While caution must be taken when analyzing sizes of solvated supramolecular architectures using DLS, qualitative comparison of particle sizes that emanate from identical building block aggregation can provide information onto the possible evolution of assembly metrics after redox-treatment. As evidenced in Figure S12 and S13 that present DLS measurements of PDI-(H)2-OH and PDI(OTEG)2-OH assemblies before and after redox-treatment, no conclusive change of particle sizes is detected suggesting that redox-assisted self-assembly does not perturb nanostructure topology. As DLS experiments could not provide any insightful information, we then investigated any structural modifications using AFM. Figure S18 compares the solid-state morphology of initially prepared and redox-treated PDI(OTEG)2-OH assemblies. No drastic differences can be gleaned as both solid-state assemblies can be described as “worm-like” structures. Height profiles ranging from 3 to 8 nm indicate that these nanoscale objects are built from one to

Table 1. Oscillator strength of the 0,0 and 0,1 transitions alongside calculated exciton bandwidth (ExBW) for PDI(OTEG)2-OH and PDI-(H)2-OH assemblies. Oscillator Strength

Building Block

PDI-(H)2-OH

PDI(OTEG)2-OH

ExBW

0,0

0,1

Initially Prepared Assembly

0.070

0.195

290 meV

Redox-Treated Assembly

0.022

0.099

380 meV

0.060

0.301

0.043

0.226

Initially Prepared Assembly Redox-Treated Assembly

402 meV 425 meV

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two bay-functionalized PDI building blocks stacking up along a 1-dimensional axis. The similar solid-state morphologies combined with the lack of substantial free-exciton bandwidth increase previously established for PDI-(OTEG)2-OH assemblies confirm that redox-assisted self-assembly does not perturb structure-function properties of these superstructures. In contrast, modification of the solid-state morphologies when comparing initially prepared and redox-treated PDI-(H)2-OH assemblies can be evidenced in Figure 5A and 5B. Additional AFM images are presented in Figure S15 and S16. While mainly amorphous domains characterized the morphology of initially prepared PDI-(H)2-OH assemblies, “worm-like” structures can be observed for the redox-treated assemblies. These PDI-(H)2-OH solid-state morphologies combined with free-exciton bandwidth enhancement observed in redoxtreated assemblies suggest that redox-assisted self-assembly perturbs, to some extent, the conformation of redox-treated PDI-(H)2-OH assembly. Please note that as all the investigated AFM samples originate from drop-casted solution, local concentration effects can assist further aggregation of solvated structures. In this regard, the solid-state morphologies of deposited materials are highly dependent on the conformation of supramolecular architectures present in solution. In agreement with the EAS, DLS and AFM data presented so far, reductive titration followed by neutral ground-state recovery of intermediate PDI-(H)2-OH assembly 1 provides formation of superstructures trapped in a kinetic state. When compared to parent assembly, redox-treated PDI-(H)2-OH superstructure experiences a conformational change leading to the emergence of novel electronic properties. In addition to spectroscopic evidences, comparison of the PDI-(H)2-OH

solid-state morphologies before and after redox-treatment equally bolsters perturbation of the superstructure conformation. This change of structure-function properties can be related to the electronic structure of intermediate state 1 shown in Scheme 1. While spectral signatures of reduced PDI(OTEG)2-OH assemblies are more reminiscent to that of partially aggregated PDI dianion, EAS of intermediate PDI-(H)2OH assembly 1 reveals the emergence of a novel electronic state that appears to be crucial to navigate the self-assembly energy landscape and enforce exciton bandwidth enhancement evidenced in redox-treated PDI-(H)2-OH assembly. It is important to note that our observations are in line with theoretical models developed for PDI-based aggregates that posit that even minor conformational change on the Angstrom scales drastically altered the short-range exciton coupling and photophysical properties of supramolecular assemblies.48 To further investigate the extent to which intermediate PDI(H)2-OH assembly can modulate final superstructure properties, thermal energy input was utilized to perturb the electronic and structural properties of reduced assembly 1 as illustrated in Scheme 1 – step 2’. Typical experiments consist of forming reduced PDI-(H)2-OH assembly (intermediate state 1) using conditions described in the experimental section followed by excursion to 90°C. The sample was then stabilized for 5 min and electronic absorption spectra were recorded during the descent to room temperature. As represented in Figure 4, spectral signatures of reduced PDI-(H)2-OH assembly at high temperature (90°C) are reminiscent to that of solubilized PDI radical dianion species and suggest dismantlement of the parent, room temperature PDI-(H)2-OH assembly.49 While a high-energy barrier enforces cohesion of the reduced PDI(H)2-OH assembly at room temperature, energy input (heat) combined with electrostatic repulsion between negatively charged building blocks bolster formation of solubilized PDI dianion species. Noteworthy is the fact that absorption profiles recorded at 20˚C before and after heating cycle differ to some extent. An overall decrease of absorptivity can be observed in the visible spectrum window, and small particles can be seen by unaided eyes after 5 minutes at room temperature. Upon cooling, solubilized dianion building blocks assemble back into charged supramolecular polymer with a structure that may differ from that of the initially reduced assembly (intermediate 1 – scheme 1). As revealed by the temperature-dependent degree of aggregation presented in Figure S14, isodesmic supramolecular polymerization best described the self-assembly of solubilized dianion with a chain elongation constant Ke of 8.5 105 Mol-1 at 298 K and a standard enthalpy change of -150 kJ mol-1. As illustrated in Scheme 1- step 4’, neutral groundstate recovery upon exposure to ambient atmosphere finalizes this redox cycle and provides reconfigured PDI-(H)2-OH superstructure. Surprisingly, analysis of solubilized superstructures aged over a course of 18 hours reveals formation of larger size particles (460 nm) when compared to redox-treated assembly (261 nm). The apparent increase of particle size is exclusively observed for PDI-(H)2-OH assemblies subjected to dismantlement-reassembly process and indicates that superstructures created immediately after neutral ground state recovery initiate formation of larger size architectures. Such structural modification suggests that intermediate PDI-(H)2OH assembly 2 assists the reconfiguration of initially prepared PDI-(H)2-OH assembly.

Figure 4. Ground state electronic absorption spectra of reduced PDI assembly as a function of temperature. Considering the instability of sodium dithionite at high temperature, 15 eq. were initially added at 20°C. Experimental conditions: [PDI-(H)2-OH] ∼0.23 mM; argon atmosphere; T = 20°C; optical path length 2mm.

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Figure 5. Topographic intermittent contact mode AFM images of: A) initially prepared PDI(H)2-OH assembly; B) redox-treated PDI-(H)2-OH superstructures; C-D) reconfigured PDI(H)2-OH superstructures. E) Corresponding height profile along the line numbers indicated on C and D. Height profile 2 (2.8 nm) corresponds to the width of one PDI unit and highlights an elementary nanowire that constructs hierarchical fibers.

While reconfigured PDI-(H)2-OH superstructures manifest free-exciton bandwidth (ExBW = 383 meV) identical to that recorded for redox-treated assembly (ExBW = 380 meV), a drastic modification of the solid-state morphology adopted by these superstructures is unveiled by Figure 5 C-D and Figure S17 that capture the formation of long aspect ratio nanowires spanning micro-to-mesoscale dimensions. Height profiles ranging from 3 nm to 8 nm combined with geometry optimization of PDI-(H)2-OH building blocks at the DFT level of theory (Figure S19) suggest that the smallest structure diameter of 3 nm corresponds to a single PDI repeating unit and defines individualized nanowires. Evolution of PDI-(H)2-OH nanowires into larger hierarchical materials is crystallized in Figure 5D where association of individualized nanowires pro-

vides formation of fiber-like materials characterized by diameters ranging from 30 to 50 nm. It is important to note that hierarchical materials presented in Figure 5 C-D and Figure S17 are exclusive to reconfigured PDI-(H)2-OH superstructure. Initially prepared and redox-treated assemblies do not provide access to such hierarchical materials and suggest that intermediate state 2, through which to navigate the self-assembly free energy landscape, plays a cardinal role in governing the structure-function relationship of final superstructures.

CONCLUSION In summary, reconfiguration of initially prepared PDI-based supramolecular polymers using redox-assisted self-assembly enables the formation of hierarchical materials equipped with

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emergent structure-function properties not accessible in parent architectures. Using a chemical reductant, injection of negative charge carriers into PDI-(H)2-OH assembly assists the formation of intermediate states from which to form supramolecular architectures trapped in a local energy minimum after neutral ground-state recovery. Superstructures created in this manner manifest free-exciton bandwidth (ExBW = 380 meV) 30% larger than that of parent equilibrium assembly (ExBW = 290 meV) therefore indicating modification of the electronic coupling between PDI-based building blocks. In sharp contrast, negligible free-exciton bandwidth enhancement after redox-treatment of initially prepared assemblies built from bay-functionalized PDI-(OTEG)2-OH underscores not only important design principle but also the cardinal role played by intermediate states in reconfiguring assembly conformation. Furthermore, temperature treatment of reduced PDI-(H)2-OH assembly enforces formation of novel intermediate state, namely PDI dianion species, which reassemble into larger superstructures upon cooling as probed by dynamic light scattering. As further evidenced by atomic force microscopy, the dismantlement-reassembly process of intermediate PDI-(H)2OH assembly creates solubilized superstructures which evolve in the solid state into hierarchical materials that feature individualized organic nanowires spanning the micro-tomesoscale dimensions. We posit that the ability to modify superstructure morphology and electronic properties paves the way to engineer a new class of optoelectronic materials.

PDI-(OTEG)2-NMe2. A solution of triethylene glycol monomethyl ether (0.15 mL, 0.94 mmol) dissolved in 5 mL THF was added dropwise to a flask under argon containing NaH (50 mg of 57%, 1.08 mmol). The mixture was stirred for 5 min at room temperature and a solution of PDI-(Br)2-NMe2 (0.25 g, 0.36 mmol) in 10-15 mL dry THF was added dropwise over a 10 min period. The mixture was stirred for 20 h at room temperature and the solvent was removed under reduced pressure. The crude product was purified by column chromatography over deactivated silica gel (dichloromethane/methanol/triethylamine 95:4:1). After removal of solvent under reduced pressure, the compound was obtained as a violet solid (201 mg, 0.234 mmol, 65%). 1H NMR (400 MHz, CDCl3) δ = 9.67 (d, 2H, J = 8.1 Hz), 8.53 (d, 2H, J = 8.6 Hz), 8.40 (s, 2H), 4.61 (m, 4H), 4.39 (t, 4H, J = 7.3 Hz), 4.11 (m, 4H), 3.88 (m, 4H), 3.79 (m, 4H), 3.70 (m, 4H), 3.57 (m, 4H), 3.36 (s, 6H), 2.75 (m, 4H), 2.42 (s, 12H). FT-IR: ῡ = 3161, 2882, 1688, 1648, 1590, 1564 cm-1. ESI-MS m/z: 429.20 [PDI-(OTEG)2-NMe2 + 2H+]2+ (calcd 429.20), 857.39 [PDI-(OTEG)2-NMe2 + H+]+ (calcd 857.39). PDI-(OTEG)2-OH. A solution of PDI-(OTEG)2-NMe2 (0.21 g, 0.25 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (0.2 mL, 1.3 mmol) and 2-bromoethanol (1.5 mL, 21 mmol) was heated under stirring at 100 °C overnight. After cooling to room temperature, 200 mL of THF was added and the resulting precipitate was collected by suction filtration and washed with 3 x 200 mL THF. The solid was then dissolved in methanol and passed through a filter paper. The clear methanol solution was evaporated under reduced pressure to yield a dark purple solid (0.16g, 0.14 mmol, 58%). 1H NMR (400 MHz, d6DMSO) δ = 9.75 (d, 2H, J = 8.3 Hz), 8.49 (d, 2H, J = 8.8 Hz), 8.44 (s, 2H), 5.37 (t, 2H, J = 4.2 Hz), 4.68 (m, 4H), 4.53 (m, 4H), 4.04 (m, 4H), 3.94 (m, 4H), 3.77 (m, 4H), 3.72 (m, 4H), 3.65 (m, 4H), 3.60 (m, 4H), 3.55 (m, 4H), 3.41 (m, 4H), 3.17 (s, 12H). UV-vis (D2O): λ nm (ε, M-1 cm-1) 506 (13650), 547 (31100), 591 (15750). ESI-MS m/z: 473.22 [PDI-(OTEG)2OH - 2Br-]2+ (calcd 473.23). Redox-Treated Superstructures. A solution of 500 µL of initially prepared PDI-(H)2-OH or PDI-(OTEG)2-OH assemblies in D2O (concentration range from 0.18 mM to 0.23 mM) was placed in a 2 mm spectroscopic cell and was further degassed under a gentle flow of argon over 30 minutes. Following which, 0 to 200 µL of a basic solution of Na2S2O4 ([1.10 mM], pH 12, sodium hydroxide) were added and the corresponding electronic absorption spectra were recorded at 20°C. Please note that during titration, the color gradually evolves from red (neutral state) to dark blue (aggregated monoanion). Upon exposure to ambient atmosphere by opening the spectroscopic cell to let ambient oxygen diffuse during 5 minutes, the reduced assemblies were oxidized back to neutral ground-state to yield corresponding redox-treated PDI-(H)2-OH or PDI(OTEG)2-OH superstructures. Please note that to assist diffusion of ambient oxygen the cell is shaken vigorously. Reconfigured Superstructures. A solution of 500 µL of equilibrium PDI-(H)2-OH or PDI-(OTEG)2-OH assemblies in H2O (concentration range from 0.18mM to 0.23mM) was placed in a 2 mm spectroscopic cell and was further degassed under a gentle flow of argon over 30 minutes. Following which, 20 µL of a basic solution of Na2S2O4 in H2O ([36.1 mM], pH 12, sodium hydroxide) were added and corresponding electronic absorption spectra were initially recorded at 20°C; the solution turned immediately dark blue, and when

EXPERIMENTAL SECTION Materials and Instrumentation. Unless otherwise noted, all chemicals were used as received. Air sensitive compounds were handled in Braun Labmaster DP glove box. N,Ndimethylformamide (DMF) and N,N-dimethylacetamide (DMA) were dehydrated by activated molecular sieves.50 Standard Schlenk techniques were employed to manipulate air-sensitive solutions. Tetrahydrofuran (THF) was distilled from Na/4-benzophenone, under argon. All NMR solvents were used as received from Cambridge Isotope Laboratories, Inc. Sodium hydroxide was purchased from Alfa Aesar. Perylene-3,4,9,10-tetracarboxylic dianhydride was obtained from Acros Organics. Sodium dithionite, methacrylate anhydride and triethylamine were purchased from Sigma-Aldrich. Triethylene glycol monomethyl ether was purchased from EMD Millipore. Bromine and iodine were obtained from Beantown Chemical. N,N-dimethylethylenediamine, 2bromoethanol, 1,8-diazabicyclo[5.4.0]undec-7-ene, 4- dimethylaminopyridine and N,N-dimethylacetamide (DMA) were purchased from Tokyo Chemical Industry. N,Ndimethylformamide (DMF), methanol, tetrahydrofuran (THF), dichloromethane and sulfuric acid were purchased from VWR. Starting materials PDI-(H)2-NMe2 and PDA-Br2-NMe2 presented in Scheme S1 and S2 were prepared according to published procedures.51-52 Flash column chromatography was performed on the bench top, using silica gel (VWR, 70-90 µm). NMR spectra were recorded on an Advance Bruker 400 MHz spectrometer. UV-vis-NIR spectra were recorded on a Cary 5000. IR spectra were recorded on a Perkin Elmer Frontier FTIR. AFM images were recorded on an Agilent 5120. DLS data were recorded on a Zetasizer Nano ZS. Mass spectra were obtained on a MicroQ-TOF ESI mass spectrometer. Preparation of PDI-(H)2-OH and PDI-(OTEG)2-OH. These building blocks were prepared following the synthetic steps in Scheme S1 and S2 in the supporting information.

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This work was made possible by University of Miami Startup Fund.

shaken vigorously, small blue particles could be visible by unaided eyes. The temperature was then ramped to 90°C (20°C min-1), and the solution was let to equilibrate during 5 minutes following which the first spectrum was recorded. During the descent to room temperature (20°C min-1), spectra were recorded every 10°C after letting the solution equilibrate for 5 minutes at each step. When cooled to 20°C, the solution was exposed to ambient atmosphere by opening the spectroscopic cell to let ambient oxygen diffuse during 5 minutes and yield corresponding reconfigured PDI-(H)2-OH superstructures. Free-Exciton Bandwidth Calculation. Theoretical model developed for H-aggregates in semiconducting polymers was utilized and is shown in equation 1.45, 53 Please note the Huang-Rhys factor has been calculated from Figure S1 (λ2 = 0.73).

ACKNOWLEDGMENT The authors thank Prof. Roger Leblanc for his assistance with Atomic Force Microscopy, and Prof. Marc Knecht for his assistance with Dynamic Light Scattering measurements. We thank Adam Ashcraft for his comment on the manuscript.

REFERENCES 1. Roznyatovskiy, V. V.; Carmieli, R.; Dyar, S. M.; Brown, K. E.; Wasielewski, M. R., Photodriven Charge Separation and Transport in Self-Assembled Zinc Tetrabenzotetraphenylporphyrin and Perylenediimide Charge Conduits. Angew. Chem. Int. Ed. 2014, 53, 34573461. 2. Würthner, F.; Saha-Möller, C. R.; Fimmel, B.; Ogi, S.; Leowanawat, P.; Schmidt, D., Perylene Bisimide Dye Assemblies as Archetype Functional Supramolecular Materials. Chem. Rev. 2016, 116, 962-1052. 3. Moulin, E.; Cid, J.-J.; Giuseppone, N., Advances in Supramolecular Electronics – From Randomly Self-assembled Nanostructures to Addressable Self-Organized Interconnects. Adv. Mater. 2013, 25, 477-487. 4. Diegelmann, S. R.; Gorham, J. M.; Tovar, J. D., OneDimensional Optoelectronic Nanostructures Derived from the Aqueous Self-Assembly of π-Conjugated Oligopeptides. J. Am. Chem. Soc. 2008, 130, 13840-13841. 5. Li, X.-C.; Sirringhaus, H.; Garnier, F.; Holmes, A. B.; Moratti, S. C.; Feeder, N.; Clegg, W.; Teat, S. J.; Friend, R. H., A Highly πStacked Organic Semiconductor for Thin Film Transistors Based on Fused Thiophenes. J. Am. Chem. Soc. 1998, 120, 2206-2207. 6. Mtangi, W.; Tassinari, F.; Vankayala, K.; Vargas Jentzsch, A.; Adelizzi, B.; Palmans, A. R. A.; Fontanesi, C.; Meijer, E. W.; Naaman, R., Control of Electrons’ Spin Eliminates Hydrogen Peroxide Formation During Water Splitting. J. Am. Chem. Soc. 2017, 139, 2794-2798. 7. Martinez, C. R.; Iverson, B. L., Rethinking the term "pistacking". Chem. Sci. 2012, 3, 2191-2201. 8. Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey, R.; Brédas, J.-L., Charge Transport in Organic Semiconductors. Chem. Rev. 2007, 107, 926-952. 9. Liu, C.; Huang, K.; Park, W.-T.; Li, M.; Yang, T.; Liu, X.; Liang, L.; Minari, T.; Noh, Y.-Y., A unified understanding of charge transport in organic semiconductors: the importance of attenuated delocalization for the carriers. Mater. Horiz. 2017, 4, 608-618. 10. Korevaar, P. A.; George, S. J.; Markvoort, A. J.; Smulders, M. M. J.; Hilbers, P. A. J.; Schenning, A. P. H. J.; De Greef, T. F. A.; Meijer, E. W., Pathway complexity in supramolecular polymerization. Nature 2012, 481, 492-497. 11. Fukui, T.; Kawai, S.; Fujinuma, S.; Matsushita, Y.; Yasuda, T.; Sakurai, T.; Seki, S.; Takeuchi, M.; Sugiyasu, K., Control over differentiation of a metastable supramolecular assembly in one and two dimensions. Nat. Chem. 2016, 9, 493-499. 12. Ogi, S.; Stepanenko, V.; Thein, J.; Würthner, F., Impact of Alkyl Spacer Length on Aggregation Pathways in Kinetically Controlled Supramolecular Polymerization. J. Am. Chem. Soc. 2016, 138, 670-678. 13. Leira-Iglesias, J.; Sorrenti, A.; Sato, A.; Dunne, P. A.; Hermans, T. M., Supramolecular pathway selection of perylenediimides mediated by chemical fuels. Chem. Commun. 2016, 52, 9009-9012. 14. Korevaar, P. A.; de Greef, T. F. A.; Meijer, E. W., Pathway Complexity in π-Conjugated Materials. Chem. Mater. 2014, 26, 576-586. 15. Korevaar, P. A.; Newcomb, C. J.; Meijer, E. W.; Stupp, S. I., Pathway Selection in Peptide Amphiphile Assembly. J. Am. Chem. Soc. 2014, 136, 8540-8543. 16. Micali, N.; Engelkamp, H.; van Rhee, P. G.; Christianen, P. C. M.; Scolaro, L. M.; Maan, J. C., Selection of supramolecular chirality by application of rotational and magnetic forces. Nat. Chem. 2012, 4, 201207. 17. van der Zwaag, D.; Pieters, P. A.; Korevaar, P. A.; Markvoort, A. J.; Spiering, A. J. H.; de Greef, T. F. A.; Meijer, E. W., Kinetic Analysis as a Tool to Distinguish Pathway Complexity in Molecular Assembly: An Unexpected Outcome of Structures in Competition. J. Am. Chem. Soc. 2015, 137, 12677-12688.

Where and correspond to the oscillator strength of the first two vibronic transitions 0,0 and 0,1 respectively; W corresponds to the free-exciton bandwidth (ExBW); and is the energy associated to a symmetric ring-stretching mode (180 meV). AFM Sample Preparation. Prior to deposition, silicon chips were washed with isopropanol and acetone. Suspension of solubilized assemblies in D2O were drop-casted and the chip was covered to limit solvent evaporation. After 30 minutes, the cover was removed and the samples were left under ambient atmosphere for an additional 2 hours. The residual water droplets were washed with D2O and the chips were dried under high vacuum overnight. Computational Methods. Geometry optimization and electrostatic potential maps of selected PDI precursors were calculated using density functional theory (DFT/⍵B97XD/ccpvdz).

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI:XXXX/XXXX Synthesis of PDI-(H)2-OH building block. Redox titrations of micelle-encapsulated PDI-(H)2-OH, and PDI-(OTEG)2-OH. Exciton bandwidth of control and equilibrium assemblies. Atomic force microscopy for all materials engineered. DLS data, NMR and High-resolution MS. (PDF)

AUTHOR INFORMATION Corresponding Author * J.-H. Olivier. E-mail: [email protected]; Phone: +1 (305) 284-3279 ORCID Jean-Hubert Olivier: orcid.org/0000-0003-0978-4107

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Funding Sources

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